ROTOR FOR A DYNAMIC FILTER SYSTEM

Abstract: A dynamic filter system having a rotor with retractable shearing elements is disclosed. The shearing elements are mounted to a shearing element support of the rotor and are displaceable between a retracted position in which said shearing elements are within a predetermined first periphery of said shearing element support, and an operative position in which said shearing elements are radially protruding from said shearing element support and extend within a predetermined second periphery of said shearing element support.

Description: Rotor for a dynamic filter system The invention relates to a rotor for a dynamic filter system. The inven- ιo tion also relates to a dynamic filter system. Furthermore, the invention relates to a filtration method and a method to install or remove a filtra¬ tion element of a dynamic filter system. Conventional dynamic filter systems have a rotor which comprises a shaft to which a plurality of si ring discs are mounted. The shearing discs are interleaved between s the filter elements of the dynamic filter system when said rotor is mounted therein with a gap maintained between each filler element and said shearing discs. The shearing discs are arranged to rotate with respect to the filter elements. Q While the shearing discs are rotating, a process fluid is pumped into the housing through a process inlet. The process fluid then passes through the gaps between the shearing discs and the filter elements. The permea¬ te passes through the filter elements and exits the housing through a permeate outlet. The retentate exits the housing through a retentate outlet. Maintenance of some dynamic filter systems is complex since access to individu. 1 filter elements requires a complete disassembly of the entire dynamic filter assembly including the rotor. Therefore, maintenance is both technically difficult and time consuming. The efficiency of shearing discs is relatively low since a laminar flow of the process fluid is generated in the gaps between a shearing disc and the surface of a filter element. Strongly varying flow conditions and velocities across the radius of the filter elements cause that some areas of the filter elements are subjected to fouling earlier than others which again causes an undesirable mainte¬ nance problem. It is therefore an object of the invention to provide a rotor for a dynamic filter system that can be removed from or inserted into said dynamic filter system without disassembling the entire filter assembly. It is another object to provide a dynamic filter system which provides more homogenous flow velocities across its radius. A further object of this invention is to provide a dynamic filter system having a rotor and one or more filter elements in which the rotor can be readily removed and inserted again without disassembly of the entire dynamic filter system, or conversely, to provide a dynamic filter system in which the filter elements, preferably in the form of a pack, can be axially removed, particularly without disassembly of the rotor. A yet further object of the invention is to provide a method for removing a rotor carrying one or more shearing elements which method is both simple and fast. A still further object of the invention is to provide a filtration method. In accordance with a first aspect of this invention there is provided a rotor for a dynamic filter system. It comprises a shearing element sup¬ port to which there is coupled at least one shearing element for a filter shear region adjacent a filter element of the dynamic filter system. The shearing element is displaceable between a retracted position in which the rotor has a predetermined first periphery and an operative position in which the shearing element radially protrudes from the predetermined first periphery and the rotor has a predetermined second periphery substantially larger than the first periphery. In a preferred embodiment the rotor comprises a shearing element support to which at least one shearing element for each of a plurality of filter shear regions each being defined by a pair of adjacent filter elements of a dynamic filter system, is movably mounted. Each shearing element is displaceable between a retracted position and an operative position. In the retracted position into which the shearing elements will be brought when the rotor is to be removed from or inserted into the dynamic filter system, said shearing elements are within a predetermined first periphery of said shearing element support. In the operative position said shearing elements are radially protruding from said predetermined periphery of said shearing element support so as to extend into said shear regions when mounted in said dynamic filter system. Then, said shearing elements are within a predetermined second periphery of said shearing element support. Said second periphery is substantially larger than said first periphery. In a preferred embodiment, the shearing elements are mounted to said shearing element support so as to be pivotable about pivot axes between said retracted position and said operative position. Said pivot axes and the rotational axis of the rotor are preferably substantially parallel to each other. Preferably, the shearing element support comprises a hollow shaft having a plurality of protrusions. Said shearing elements are hingedly mounted between said protrusions. It is preferred that said shearing elements are within the periphery of said protrusions when in said retracted position. In an embodiment, the hollow shaft is capable of conducting at least part of the fluid flow to said dynamic filter system. In a preferred embodiment, the rotor has means for displacing said shearing elements between said retracted position and said operative position. The displacing means preferably comprise a spring which forces the shearing elements into its retracted and/or into its operative position. Most preferably the arrangement is such that the same spring will force the shearing elements both into a stable retracted and into a stable operative position. Preferably 2, 3, 4, 5 or 6 shearing elements arranged in rotational symmetry are employed. It is, however, within the scope of this invention to employ only one shearing element at a given axial position of the shearing element support or to employ a plurality of shearing elements arranged asymmetrically around the shearing element support. The rotor preferably also has locking means for securing said shearing elements in either said retracted or said operative position. Preferably, said shearing elements have the form of blades that radially extend from said shearing element support when in their operative position. It is even more preferred that the blades are sickle-shaped. This is particularly advantageous when said shearing elements are hinged- ly mounted on said shearing element support. Then, the shearing ele¬ ments are mounted in such way that the bow of the sickle-shaped shearing element essentially winds around an axis of said shearing ele¬ ment support when in said retracted position. It is preferred to provide at least two shearing elements to be operated in one filter shear region. It is advantageous to arrange the shearing elements in rotational symmetry. In a second aspect of the invention, there is provided a dynamic filter system comprising a plurality of disc-shaped filter elements forming a stator of the dynamic filter system, and a rotor. Each filter element has an aperture essentially at its center. The plurality of filter elements is arranged upon one another at predetermined distances. The spaces between adjacent ones of said filter elements define filter shear regions. The rotor of said dynamic filter system has a shearing element support to which a plurality of shearing elements is mounted. Said shearing elements radially extend into respective ones of said plurality of filter shear regions and have the form of blades. The filter elements which are generally disc shaped may be comprised of two or more filter sectors and/or the stack of filter elements may comprise two or more stacks of sector shaped filter elements. The preferred structure of the rotor is such that the shearing elements in their retracted position are within the periphery of the shearing element support. This arrangement protects both the shearing elements and the filter elements when the rotor is axially moved relative to the filter elements. It is, however, within the scope of this invention that the shearing elements in their retracted position are spaced completely or partially radially outwardly from the periphery of the shearing element support. In a preferred embodiment, the blade-like shearing elements are sickle- shaped. Preferably, there are provided at least two blade-like shearing elements for each shearing region. The sickle-shaped shearing elements are then preferably arranged in rotational symmetry. In accordance with a further aspect of this invention, there is provided a dynamic filter system which comprises at least one disc shaped filter element with an aperture essentially at its center. This aperture together with flanges (if any) or the like, holding the filter material, forms an area without filtration, which area has a diameter D R . The shearing elements in their operating position inscribe an area having a diameter D B . In accordance with a preferred embodiment of this invention the ratio of the diameters D B /D R is not greater than about 3. Preferably, the ratio of diameters D B /D R is greater than 1,5. In an even more preferred embodiment, the ratio of diameters D B /D R is also less than 2,6. It is preferred that the ratio of diameters D B /D R is equal for all individual shearing regions. The preferred dynamic filter system comprises a plurality of disc-shaped filter elements forming a stator of the dynamic filter system, and a rotor. Each filter element has an aperture essentially at its center. The plurality of filter elements is arranged upon one another at predetermined dis¬ tances. The spaces between adjacent ones of said filter elements define filter shear regions. A plurality of shearing elements is mounted to the shearing element support which shearing elements extend into respective ones of said plurality of filter shear regions. When the ratio of diameters D B /D R is set to be no more than 3 for each filter shear region for this embodiment of the invention a relatively uniform flow of fluid over the filter elements is achieved. In a particularly preferred embodiment of both the second and third aspect of the present nvention, the rotor of the dynamic filter system has shearing elements vhich are displaceable between a retracted posi¬ tion and an operative position as defined by a rotor according to the first aspect of the invention. The shearing elements, in accordance with a yet further preferred em¬ bodiment of this invention, have such a configuration of the surface, which is parallel to the corresponding filter surface, that the circumferential length (1) thereof increases with increasing distance (r) from the axis of rotation of the rotor. Preferably this relationship is linear, and most preferably the circumferential length (1) is proportional to this distance (r) from this axis of rotation. In this preferred embodi¬ ment, the increase in circumferential length exists over the major portion of the functional area of the shearing elements. At the outer end and the inner end (i.e. for example outside the functional area or the area of shearing elements facing the filter area, respectively) the shearing elements can be rounded and the mentioned relationship does not have to exist in these areas. Other features and advantageous effects of the present invention will become apparent when reading the following description of preferred embodiments in conjunction with the drawing, in which Fig. 1 shows a sectional schematic view of a dynamic filter system having a rotor according to a preferred embodiment of the present invention; Fig. 2 illustrates a preferred embodiment of the present invention with the shearing elements being in said operative position; Fig. 3 illustrates another preferred embodiment of the present inven¬ tion having three shearing elements per shearing region; Fig. 4 illustrates still another preferred embodiment of the present invention having four shearing elements per shearing region. Fig. 5 illustrates the configuration of the functional surface of a shear¬ ing element depending on the length of the periphery (1) and a given radius (r). Fig. 1 shows a dynamic filter system in sectional view according to an embodiment of the second aspect of the invention. The illustrated dyna¬ mic filter system employs a rotor according to a preferred embodiment of the—first aspect of the present invention. The dynamic filter system has a process fluid inlet 8, a filtrate outlet 9 and a retentate outlet 10. Typically, the process fluid inlet 8 is at a central portion of the dynamic filter system whereas the outlets 9, 10 are at a peripheral portions thereof. The rotor is shown with shearing elements 3 in their operative position such that they extend into shearing regions of the filter assembly. The shearing regions are defined by a gap between every two adjacent filter elements 5 of a plurality of filter elements 5 arranged in a stack. The filter elements 5 are disc-shaped with a central aperture. Each of the shearing elements 3 is pivotably mounted to a shearing element support 1 using disc-shaped protrusions 7 extending from the outer surface of a hollow shaft 2 which also serves as a conduit for at least part of the fluid flow to the dynamic filter element. A set of shearing elements is hingedly connected to said protrusions 7 by a bolt 4 extending through said protrusions 7 and said set of shearing elements. This way each shearing element of said set of shearing elements 3 has the same angular position with respect to the axis of said shearing element support 1. In Fig. 1 the rotor of this embodiment is shown to have two sets of shearing elements 3 opposing each other with respect to the axis of said shearing element support 1. Then, said two sets of shearing elements 3 are spaced apart by an angle of 180 degrees with respect to the rotational axis of the rotor. The diameter of the area without filtration, i.e. the diameter of this inner space is D R . This inner space is generally approximately equal to the central opening in the filter element. Fig. 2 shows a plane view of an embodiment of a rotor of the present invention having two sets of shearing element 3. The rotor is viewed in direction of its rotational axis. Two shearing elements 3 are shown to be in their operative position such that they extend over the periphery of disc-shaped protrusions 7. The retracted position of the shearing elements 3 is indicated with dashed lines. The shearing element support 1 is shown to have a diameter of D R . This is for illustration purposes. The diameter D R actually relates to that of the non-filtration-region, which only approximately equals that of the rotor with retracted shearing elements. This rotatable support 1 and the shearing elements 3 at their operative positions inscribe a circular area of diameter D B . Typically, the outer diameter D F of the disc-shaped filter elements 5 will be larger than the diameter D B . Typically, the diameter of the central aperture of the disc-shaped filter elements will be larger than the diameter D R of the shearing element support. In the arrangement of fig. 2 a ratio of diameters of D B /D R of 2.58 is realized. The shearing elements 3 are blades having a sickle-shaped curvature. At one end each set of shearing elements 3 is hingedly mounted to said protrusions 7 by a bolt 4. The outer curve of each sickle-shaped shearing element 3 has essentially about the same radius of curvature as the outer radius of said disc-shaped protrusions 7. The length of the outer curve is about half the perimeter of said disc-shaped protrusions 7. The shearing elements 3 may be fixed in their operative position by a rod 6 that extends through said protrusions 7 and said shearing elements through respective aligned bores therein. The length of said rod 6 corresponds to the length of said bolt 4. Preferably, bolt 4 and rod 6 run parallel to the rotational axis of the rotor. Alternatively, a stop may be provided against which each shearing element rests with a force that is generated when the shearing elements are moved through the process fluid. This force depends on the viscosity of the process fluid. Preferably the stop and the engaging section of the shearing element are adapted to fix securely and precisely the position of the shearing elements, in particular, relative to the filter surfaces. Another embodiment of a rotor is shown in Fig 3. This embodiment corresponds to the one shown in Fig 2 except that there are three sets of shearing elements 3. The sets of shearing elements 3 are spaced apart by an angle of 120 degrees with respect to the rotational axis of the rotor, thereby achieving rotational symmetry. The fact that there are three shearing elements in each shearing region enhances the shearing effect in the shearing regions. Also, the ratio of diameters D B /D R is reduced to 2,36 thereby achieving a more evenly distributed flow velocity across the radius of the shearing elements. Fig. 4 shows a still further embodiment of the present invention having four sets of shearing elements arranged in rotational symmetry with a 90° angle spread. In this embodiment the shearing elements are shaped to extend, when in their retracted position, effectively more than one fourth over the perimeter of the shearing element support. This embodi¬ ment has a ratio of diameters D B /D R of 2,22. The blade-like shearing elements 3 of the present invention may be of any cross-sectional shape. It will be advantageous to provide a cross- sectional shape that particularly improves the shearing effect. The surface of the blades can be contoured to enhance the generation of turbulence in the shearing regions. As shown in Fig. 5 representing an embodiment of this invention, the shearing elements 3 have a configuration of then- functional surface, i.e. of the surface which faces the filter surface moving relative to the filter surface with the work fluid in between the surface and the filter surface, which becomes increasingly wider as one moves radially outwardly along the shearing element. This fact can be expressed also by the relationship between the circumferential lengths (1) at a given radius (r) and as a function of this radius. The circumferential length (1) is the length of that section of a circle drawn around the rotational axis of the rotor with the radius of the respective location which extends from one edge of the shearing element to the other (see Fig. 5). The relationship between the circumferential lengths (1) and the radius (r) in accordance with this embodiment of the invention, is that the circumferential length preferably increases along a continuous curve from the innermost to the outermost radius. The innermost and outermost radius being defined as those between which the shearing element develops its major functional action. In the drawing, the preferred func- tional relationship between the circumferential length and the radius is shown. For the innermost radius (rl), an intermediate radius (r2) and the outermost radius (r3), the respective circumferential lengths 11, 12 and 13 are shown. The relationship there shown is that the circum- ferential length (1) is proportional to the radius (r) in this range. Instead of having shearing elements hinged to the shearing element support they may also be mounted to said shearing element support so as to be linearly movable between said retracted position and said operative position. The shearing elements, though illustrated as such in the figures, also do not have to be aligned in sets along the shearing element support. Instead, said shearing elements may be displaced by a predetermined angle from one shearing region to another, thereby for example allowing for a helical arrangement. Further, said shearing elements as well as said filter may be dimensioned differently for each of said shearing regions. Thereby, the dynamic filter system can be structured like a cone. In accordance with this invention there is also provided a method of filtration comprising extending the shearing elements over the filter, rotating the rotor, and passing a fluid through the filter elements. Prefer- ably this method is carried out as follows: A stack of new or cleaned filter elements is provided surrounding the rotor to which the shearing elements are coupled. The shearing elements are placed relative to the stack of filter elements in such a way that they can be extended into the gaps between the filter elements. The filter elements in this process preferably are either prearranged as a ring shaped stack and the rotor with the shearing elements in the retracted position is inserted into this stack or the stack is assembled around the rotor employing filter element sections and a frame into which these sections are inserted to result in the ring shaped stacked filter elements. Thereafter, the shearing elements are extended from the shearing ele¬ ment support and into the desired distance from the filter element. Preferably the shearing elements are locked in the desired position. Rotating the rotor with the shearing elements extended into the operat¬ ing position will cause a forced movement of the fluid and thus a dynamic filtration since the fluid so moved will also wash away some of the retained materials on the surface of the filter elements. When the filter elements have become sufficiently plugged or sufficiently worn the opposite procedure is performed. Preferably the blades are retracted from the operating position into the retracted position and rotor and filter elements are disassembled, preferably by axial removal of the filter element(s) relative to the rotor. Again, the filter elements can also be disassembled by removing sections thereof in the case that these filter elements are built from removable sections. In accordance with yet another embodiment a method of installing or removing the filter elements (or filter sectors) comprising retracting the shearing elements and moving the filter elements, either individually or as a group, axially along the rotor assembly. The method allows the removal and replacement of filter elements as well as the removal and replacement of shearing elements in a fast and efficient manner.

Claims: CLAIMS 1. Rotor for a dynamic filter system comprising: a shearing element support (1); at least one shearing element (3) for a filter shear region adjacent a filter element of said dynamic filter system wherein the shearing element (3) is coupled to said shearing element support and is dis¬ placeable between a retracted position, in which said rotor has a predetermined first periphery and an operative position, in which said shearing element (3) radially protrudes from said predetermined first periphery and said rotor has a predetermined second periphery substantially larger than said first periphery. 2. Rotor according to claim 1, wherein said rotor has an axis of rota¬ tion and a plurality of shearing elements are coupled to said rotor for rotation with said rotor at at least two different locations along the axis of rotation. 3. Rotor according to claim 1 or 2, wherein said shearing elements (3) are essentially pivotable about pivot (B, C) axes between said re- tracted position and said operative position and wherein said pivot axes of said shearing elements (3) are substantially parallel to the axis of rotation (A) of the rotor. 4. Rotor according to claim 2, wherein said shearing element support ( 1) comprises a hollow shaft (2) having a plurality of protrusions (7) for hingedly mounting said shearing elements (3). s 5. Rotor according to any of the preceding claims, further comprising a locking means (6) for securing said shearing elements (3) in their operative position. 6. Rotor according to any of the preceding claims, wherein said shea- o ring elements (3) have the form of blades, and/or wherein said shearing elements are contoured, in particular wherein they are sickle-shaped. 7. Rotor according to any of the preceding claims, wherein said shea- ring elements (3) are arranged in rotational symmetry. 8. Rotor according to any of the preceding claims, further comprising means (4) for displacing said shearing elements (3) between said retracted position and said operative position. 9. Rotor according to any of the preceding claims, wherein there are provided 2, 3, 4, 5 or 6 shearing elements (3) for each shearing region. 10. Rotor according to any of the preceding claims, wherein said shear¬ ing element (3) has such a configuration of the surface which is facing the corresponding filter surface, that the circumferential length (1) thereof increases with increasing distance (r) from the axis of rotation of the rotor. — l o ¬ 11. Rotor in accordance with claim 10, wherein the functional surface of the shearing element (3) is such that the circumferential length (1) is linearly related, preferably proportional to the distance from the axis of the rotor. 12. A dynamic filter system comprising: a filter element (5) having a filter surface and a rotor including a shearing element support and at least one shearing element coupled to the shearing element support, characterized in that the shearing element is displaceable between a first position spaced from the filter surface and a second position adjacent to the filter surface. 13. The dynamic filter system of claim 12, wherein the filter element includes an opening and wherein the diameter of the rotor is small- er than the opening when the shearing element is in the first posi¬ tion and the diameter of the rotor is larger than the opening when the shearing is in the second position. 14. Dynamic filter system comprising a plurality of disc-shaped filter elements (5), each filter element (5) having an aperture essentially at its center, wherein said filter elements (5) are arranged upon one another leaving predetermined distances therebetween, each pair of adjacent filter elements (5) defining a filter shear region, and said rotor having a shearing element support (1), said shearing element support (1) having at least one shearing element (3) coupled thereto which extend into respective ones of said plurality of filter shear regions, characterized in that said shearing element (3) has the form of a blade radially protru¬ ding from said shearing element support (1), in particular wherein said shearing elements are arranged as defined in claim 10 or 11. 15. Dynamic filter system according to one of claims 12 to 14, wherein said shearing element (3) is sickle-shaped. 16. Dynamic filter system according to one of claims 12 to 15, wherein there are provided 2, 3, 4, 5 or 6 shearing elements (3) for a shearing region at approximately the same axial position of the shearing element support. 17. Dynamic filter system comprising at least one disc-shaped filter element (5), each filter element (5) having an aperture essentially at its center, and a rotor having a shearing element support (1), said shearing element support (1) having at least one shearing element (3) mounted thereto which extends into a filter shear region and which inscribes an area of a diameter D B when rotating said rotor, and wherein the aperture and adjacent holders (if any) for filter material define an inner region free of filtration having a diameter DR, characterized in that the ratio of D B /D R is less than 3, preferably less than 2.6. 18. Dynamic filter system according to claim 17, wherein the ratio of D B /D R is larger than 1,5. 19. Dynamic filter system of claims 17 or 18 wherein a plurality of filter elements are arranged upon one another leaving predetermined distances therebetween, a pair of adjacent filter elements (3) defi¬ ning a filter shear region and wherein at least one shearing element extends into each shear region. 20. Dynamic filter system according to any of claims 17 to 19, wherein the ratio D B /D R is equal for each shearing region of said plurality of shearing regions. 21. Dynamic filter system according to airy of claims 17 to 20, wherein said rotor is as defined in any of claims 1 to 11. 22. A filtration method comprising: extending a shearing element to a position adjacent to a filter element; rotating the shearing element; and passing a fluid through the filter element. 23. A method for installing or removing a filter element in a dynamic filter system comprising: retracting a shearing element of a rotor and moving the filter element axially along the rotor. 24. Method of claim 22 or 23 wherein said shearing element is coupled to a rotor as defined in one of the claims relating to a rotor. 25. Method of claim 24 wherein said shearing element is pivoted around an axis via which it is coupled to a shearing element support of said rotor in order to extend it or respectively retract it.

Inventors: RANDHAHN HORST, RANDHAHN, HORST
Applicants: PALL CORP, RANDHAHN HORST, PALL CORPORATION, RANDHAHN, HORST
Application year: 1994
Main classification: B01D29
IPC codes: B01D29, B01D65